Ruggedized RFID tag and reader

ABSTRACT

A radio frequency identification (RFID) transponder tag is contained in and electrically connected to a mechanically rugged metallic tag housing slotted to define a radio frequency antenna, such as a half turn antenna, and sealed with an epoxy filling.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to the field of radio frequency identification(RFID) readers of the type used in access control systems for readingelectronically coded key tags and key cards.

2. State of the Prior Art

RFID reader/writer units may be wall mounted in access controlapplications where a RFID transponder tag is waved near the reader bypersons requesting access. One of the key elements of an RFID (RadioFrequency Identification Device) reader/writer is the antenna. Theantenna can be a metal coil or a dipole, depending on the applicationand other particulars of the system. Radio frequency power is providedto the antenna by appropriate electronic circuits of the reader in amodulated form (the carrier frequency), which is then radiated by theantenna to any proximate RF transponder tag. Radiated power from thetransmitting antenna is absorbed by the antenna of the transponder tagwhere it powers up the electronic chip of the transponder. The chip ofthe transponder then returns a coded signal detectable by the RFIDreader unit. The carrier frequency is usually used as a clock signal forthe transponder chip.

The reader communicates with the transponder by modulating the carrierfrequency in a patterned or coded manner (usually pulse positionmodulation). The transponder communicates with the reader/writer usingsimilar methods usually encompassing loading of the carrier signal byshunting the transponder antenna to effect a corresponding variation inthe reader/writer antenna. This is usually accomplished using ASK(amplitude shift key), FSK (frequency shift key), PSK (phase shift key)or various other techniques using one or more sub frequencies.

The nature of RF energy in this type of application precludes it frompenetrating an electrically conductive metal housing. Therefore, mostRFID reader/writer units are designed such that the antenna is coveredor enclosed in a non conducting material such as polycarbonate, epoxy orABS. While this design allows the antenna to send and receive, therelative weakness of these materials leaves the antenna (and anythingpackaged with it) vulnerable to vandalism and tampering. In the past,installation and maintenance of RFID reader/writers of this type in highrisk areas has been problematic.

Others have constructed reader/writers that are packaged with theantenna behind a thin metal plate with one or more narrow slits or holesin a metal plate covering the front of the reader unit. The slit(s) orhole(s) allow the radio-frequency field to propagate beyond the platefrom the antenna inside the reader enclosure. However, the metal platein these designs has thickness limitations, and as a result the addedprotection is minimal.

An example of such prior art efforts is shown in PCT Publication WO01/50423 A1 entitled “Electronic Key Reader”. In this publication theantenna is a loop mounted behind a front metal plate of the RFID tagreader housing. One or more slots in the front metal plate allowpropagation of the radio frequency field emitted by the internalantenna. However, the antenna loop is an element distinct from the metalplate or housing.

As previously explained, the RFID tags, used as identification tokens orkeys to actuate RFID readers, generally consist of a radio frequencytransponder module connected to a radio frequency antenna. The antennamay be a wire coil or may consist of one or more printed circuit loops.Typically, the transponder module and antenna are encapsulated inplastic for durability, such as in a plastic card. Existing plasticencapsulated RFID tags, while durable for use in operating doorways,elevators and garage gates in normal office, industrial and residentialapplications, are not sufficiently rugged for certain applications wheresuch tags may be subject to a much greater degree of abuse, impact andmechanical wear, for example, in military applications. A need existsfor more robust RFID tags better suited for rugged environments.

SUMMARY OF THE INVENTION

This invention addresses the problem of providing better physicalprotection against vandalism for RFID reader/writer units by providingthe units with stronger housings made of metal rather than plastics.

This invention provides a metal plate cover or housing which alsofunctions as the antenna element of the reader/writer. Since the antennais also the metal plate cover or housing, which can be virtually anythickness, improved vandal/tamper resistance is achieved withoutblocking the RF signal. According to this invention, the antenna isintegral with the metal cover or housing and not a distinct element asin the aforementioned reference.

A ruggedized RFID tag is provided having a metal tag housing slit orslotted to define a radio frequency antenna, such as a half turnantenna, and has a RFID transponder in the tag housing operativelyconnected with the antenna. An antenna matching circuit may be providedfor operatively interconnecting the transponder with the antenna. Thetag housing may be of steel, aluminum or other mechanically strong andelectrically conductive metal or alloy.

In one embodiment the metal tag housing comprises two metal housingportions joined mechanically and electrically to each other andcontaining therebetween the RFID transponder. The metal housing portionsmay be both slotted to define the antenna, and the metal housingportions may be mechanically and electrically joined by crimpingtogether along the edges of the housing portions. Electricallyinsulating material such as epoxy may be provided in each slot forclosing the slot against entry of foreign matter into the tag housing.

The tag housing may also be partially of electrically conductivematerial shaped and configured to define a radio frequency antennaintegral with the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a metal front plate for an RFID reader cut with arectangular spiral slit to define a spiral antenna integral with themetal plate;

FIG. 2 illustrates a one piece metal housing having both a metal frontand metal sides, the metal front cut with a slit to define a single turnradio frequency antenna integral with the metal housing;

FIG. 3 is a typical electrical block diagram of the ruggedized RFID tagaccording to this invention;

FIG. 4 is an exploded perspective view showing the main components of atypical ruggedized RFID tag according to this invention;

FIG. 5 is a close up view of the RFID transponder module of the tag ofFIG. 4;

FIG. 6 is a perspective view of the assembled tag of FIG. 4 showing howthe lip of the bottom housing portion is crimped over the top housingportion and also indicating the location of the RFID transponder inphantom lining; and

FIG. 7 is a cross section taken along line 7-7 in FIG. 6 showing how theRFID module is cptive between the housing portions and the elastomericconnectors contact the inside surface of the top housing portion.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention is illustrated in accompanyingFIG. 1, where a metal plate 10 is cut with a rectangular spiral slit 12to define a spiral antenna 14 integral with the metal plate 10. Theplate 10 may be of aluminum, anodized to provide electrical insulationon the aluminum surface. The insulation prevents contact and shortingbetween adjacent turns of the spiral antenna 14 and also protects usersagainst possible electrical shock in the event of a circuit malfunctionof the RFID reader/writer circuits. As indicated in the drawing theopposite ends 16 of the spiral antenna are connected to appropriatepoints of the RFID reader/writer electronic circuits such that radiofrequency energy is delivered to the antenna 14 and radiated therefrom.The metal plate provides an exterior cover, such as a front cover plate,for the circuits of a RFID reader installed in a wall or otherprotective structure which completes an enclosure with the metal plate10.

FIG. 2 of the accompanying drawings illustrates another embodiment ofthe invention where a metal housing 20 having both a metal front 22 andmetal sides 24 is cut with a slit 26 to define a single turn radiofrequency antenna 28 integral with the housing 20. Appropriate points ofthe integrated housing/antenna 20, 28, such as the opposite ends 30 ofthe single turn antenna, are electrically connected to the radiofrequency output of the reader/writer circuits for injecting the antennawith RF power. The metal front 22 and metal sides 24 of the housing ofFIG. 2 may be formed as single metal piece for greater strength. Anappropriate housing back, which may also be of metal, is provided whereneeded. The metal housing of FIG. 2 is suitable for RFID readerinstallations where the reader is free standing or is mounted to a wallsurface, for example, so that the reader is not otherwise surrounded byprotective structure. In such installations the metal housing may fullyenclose and protect the circuits and other components of the readerunit.

In both embodiments of FIGS. 1 and 2 the antenna and the metal housing20 or front plate 10 are a single integrated element which can be madeof any suitable thickness to provide a desired degree of physicalprotection against vandalism of both the antenna and any RFIDreader/writer circuits and components housed behind the metal plate 10or in the metal housing 20.

The ruggedized RFID tag 30 according to this invention is illustrated inFIGS. 3 through 7 of the drawings. FIG. 3 shows in block diagram formthe electrical circuit of RFID tag 30, including an RFID transpondercircuit 32, an antenna matching circuit 34 and a radio frequency antenna36.

FIG. 4 shows in exploded relationship the main physical components ofruggedized RFID tag 30. Tag 30 has a tag housing 40 comprised of twohousing portions, a top housing portion 42 and a bottom housing portion44. The two housing portions 42, 44 in the illustrated embodiment areflat plates, one of which has a raised lip 46 extending about the edgeof the plate.

An electrically insulating spacer plate 48 is contained between housingportions 42, 44 and within raised lip 46. Spacer plate 48 carries anRFID transponder module 50 which includes the RFID transponder circuit32 and the antenna matching circuit 34.

In the presently preferred embodiment both top and bottom housingportions 42, 44 are metallic, for example, of steel, aluminum or anyother mechanically strong metal or alloy with sufficient electricalconductivity for purposes of this application. The insulating spacer 48may be of ABS (Acrylonitrile Butadiene Styrene), PVC (Polyvinylchloride), nylon, ceramic or any electrically and mechanically stableelectrical insulator.

As seen in FIG. 5, transponder module 50 has a substrate 52 on which aremounted the electrical and electronic components which together make upthe RFID transponder circuit 32 and antenna matching circuit 34. Thetransponder circuit 32 is an integrated circuit die 54, while antennamatching circuit 34 is comprised of matching circuit components 56,which typically are surface mount capacitors. The output of antennamatching circuit 34 terminates in connections to a pair of elastomericconnectors 58 mounted on substrate 52. These connections may be by wayof conductive traces on substrate 52 or by other suitable means.

Each of the top and bottom housing portions 42, 44 are slit to define aradio frequency antenna. In the illustrated embodiment, housing portionsare slit by means of a center slot 60 extending partially along alongitudinal dimension of the housing portions and open at one end ofeach housing portion to divide and define two equal lobes 62 on eachhousing portion 42, 44.

In an assembled condition of tag 30 depicted in FIGS. 6 and 7 the topand bottom housing portions 42, 44 are joined electrically andmechanically to each other, for example, by mechanically crimping theraised lip 46 of the bottom housing portion over the top housing portion44. The crimp 68 suggested by the arrows in FIG. 6 establishes anelectrical connection extending along the crimped together edges of thehousing portions 42, 44 and also makes a strong mechanical joint betweenthe two housing portions. Other methods of mechanically joining andelectrically connecting the housing portions 42, 44, such as welding orsoldering, among others, may also be used. The top and bottom housingportions 42, 44 are joined with the corresponding slots 60 overlaid inregister with each other, that is, with the open ends 60 a of slots 60located on the same end of the tag housing 40, so that electrically thestacked slots 60 extend through the thickness of the assembled taghousing, and the two electrically connected slotted housing portions 42,44, i.e. the tag housing, acts as a single radio frequency antenna 36.The slots 60 define a half turn radio frequency antenna 36 which isdriven via the antenna matching circuit 34, so that the tag housing 40also becomes the antenna 36 for the RFID transponder 32 contained in thehousing. The tag housing 40 thus serves the dual function ofmechanically containing and protecting the RFID transponder 32 and ofreceiving and radiating RFID radio frequency signals between RFIDtransponder 32 and a suitable RFID tag reader unit.

In an assembled condition of the tag 30, the spacer plate 48 lies on thebottom housing portion 42 within raised lip 46. The substrate 52 isaffixed to the spacer plate 40 by suitable means, such as an adhesive.The top housing portion 42 lies over the spacer plate 48 and withinraised lip 46 of the bottom housing portion 44. The two housing portions42, 44 are assembled with the spacer 48 in-between to form a three layerstack, as best seen in FIG. 7. In the assembled condition the insidesurface 64 of top housing portion 44 presses down on the two elastomericconnectors 50, so that each connector 50 establishes an electricalconnection between one output side of the antenna matching circuit 34and a corresponding lobe 62 of the antenna defined by top housingportion 42. The elastomeric connectors 50 may be commercially availablesilicone elastomeric connectors of a type well known in the field.

In the assembled tag 30 it will be desirable in most applications tofill the slots 60 with a nonconductive but durable material, such asepoxy, to seal the interior of the tag 30 against entry of moisture andforeign matter. Alternatively, raised ridges may be formed integrallywith the spacer plate 48 such that the raised ridges align with and fillthe slots when the top and bottom housing portions 42, 44 are stackedwith the spacer plate 48 between them, thereby closing the slots againstentry of foreign matter. A hole 70 may be provided through the housing40 for passing a neck chain or the like.

In one embodiment, the dimensions of tag housing 40 may be 0.5 inch wideor wider, 1.0 inch long or longer, and 0.1 inch thick. In otherembodiments, the tag housing may be between 0.3 inches and 2 inches inwidth, between 0.5 inch and 3 inches in length, and between 0.05 and0.25 inch in thickness. Still larger tag dimensions may be foundsuitable for certain applications, even double or triple the precedingdimensions, for example.

The ruggedized tag 30 of this invention is suitable for operation at theRFID radio frequency of 13.56 MHz. However, it may be adapted foroperation at other frequencies as well. The design and constructions ofantenna matching circuit 34 is well understood in the RFID field andneed not be explained in greater detail here.

The housing portions 42, 44 may be of materials other than metalprovided at least a part of one housing portion is electricallyconductive so as to define a radio frequency antenna operative at therelevant RFID frequency. For example, it is contemplated that bottomhousing portion 44 could be of a mechanically strong but non conductivematerial, such as a hard ceramic, and only the top housing portion ismetallic and slit or slotted for defining an antenna. It is alsocontemplated that both housing portions could be of a nonconductive butmechanically rugged material such as a hard ceramic, and a metalliclayer deposited or applied to the interior, exterior or both of thehousing portions so as to define an antenna. Antenna 32 may take formsother than the half turn antenna shown in the drawings, and byappropriate slitting or slotting of the tag housing an antenna havingone or two turns or a spiral antenna could be defined on tag housing 40.

Other methods and means for making the electrical connection between theradio frequency transponder output and the antenna may be used inaddition to or in lieu of silicone elastomeric connectors. For example,conductive epoxy may be used for this purpose, among otherpossibilities.

While particular embodiments of the invention have been described andillustrated for purposes of clarity and example, it will be understoodthat many changes, substitutions and modifications will be apparent tothose having only ordinary skill in the art without thereby departingfrom the scope of the invention as defined by the following claims.

What is claimed as new is:
 1. In combination, an RFID tag housing havinga plurality of at least partially electrically conductive housingportions, said housing portions shaped and configured and electricallyconnected to jointly define a radio frequency radiating antennaincluding a pair of antenna lobes formed integrally with a first and asecond of said housing portions, an RFID transponder circuit containedbetween and mechanically protected by said housing portions, and anantenna matching circuit having a pair of outputs each electricallyconnected to a corresponding one of said antenna lobes operativelyconnecting said transponder circuit with said antenna.
 2. Thecombination of claim 1 wherein said housing portions are is made ofmetal.
 3. The combination of claim 1 wherein said housing portions areis made of relatively thick material for substantially protecting saidradio frequency circuits from damage caused by physical abuse of saidhousing.
 4. The combination of claim 1 wherein said housing portionshave therein one or more slots for defining said antenna lobes.
 5. Thecombination of claim 1 wherein said housing portions have one or moreslots for defining said antenna lobes and said one or more slots arefilled with nonconductive material for closing said slots against entryof foreign matter into said housing.
 6. The tag of claim 1 wherein saidhousing portions comprise two metal housing portions joined mechanicallyand electrically to each other and containing therebetween saidtransponder.
 7. The tag of claim 6 wherein said metal housing portionsare both slotted for defining said antenna lobes.
 8. The tag of claim 6wherein said metal housing portions are mechanically crimped to eachother.
 9. A ruggedized RFID tag, comprising first and secondelectrically conductive housing portions mechanically and electricallyjoined along an edge thereof and containing therebetween an RFIDtransponder circuit, said housing portions being divided by a slotextending partially along a longitudinal direction thereof and open atone end of each housing portion to define two antenna lobes, saidtransponder circuit including a pair of antenna outputs each operativelyconnected for driving a corresponding one of said antenna lobes.
 10. Theruggedized RFID tag of claim 9 wherein said first and second housingportions are metallic plates.
 11. The ruggedized RFID tag of claim 9further comprising a non-conductive substrate supported between saidmetallic plates for carrying said RFID transponder circuit.
 12. Aruggedized RFID tag comprising: a tag housing including top and bottomelectrically conductive housing portions mechanically joined andelectrically connected to each other, said portions divided by one ormore slots for defining antenna lobes of a radio frequency antenna;electrically insulating material in said one or more slots for closingeach said slot against entry of foreign matter into said housing; anelectrically insulating substrate between said housing portions, an RFIDtransponder module supported on said substrate including antenna outputsof said transponder module each connected to a corresponding one of saidantenna lobes for receiving and transmitting RFID signals by way of saidantenna.
 13. The ruggedized RFID tag of claim 12 wherein said RFIDtransponder module antenna outputs include an antenna matching circuitconnected to said antenna lobes.
 14. The ruggedized RFID tag of claim 12wherein said top and bottom housing portions are metal plates joined toeach other along edges thereof.
 15. The ruggedized RFID tag of claim 14wherein said metal plates are each slit by a center slot extendingpartially along a longitudinal dimension of said housing portions andopen at one end to divide said plates and define two said lobes of saidantenna.
 16. The ruggedized RFID tag of claim 12 wherein said top andbottom housing portions are constructed and configured to mechanicallyprotect said RFID transponder module against physical abuse of said tag.